Search Results (3)

A bootstrapping technique used to increase the intrinsic voltage gain of a bulk-driven MOS transistor is described in this paper. The proposed circuit incorporates a capacitor and a cutoff transistor to be connected to the gate terminal of a bulk-driven MOS device, thus achieving a quasi-floating-gate structure. As a result, the contribution of the gate transconductance is cancelled out and the voltage gain of the device is correspondingly increased. The technique allows for implementing a voltage follower with a voltage gain much closer to unity as compared to the conventional bulk-driven case. This voltage buffer, along with a pseudo-resistor, is used to design a linearized transconductor. The proposed transconductance cell includes an economic continuous tuning mechanism that permits programming the effective transconductance in a range sufficiently wide to counteract the typical variations that process parameters suffer during fabrication. The transconductor has been used to implement a second-order $G_m$-C bandpass filter with a relatively high selectivity factor, suited for multi-frequency bioimpedance analysis in a very low-voltage environment. All the circuits have been designed in 180 nm CMOS technology to operate with a 0.6-V single-supply voltage. Simulated results show that the proposed technique allows for increasing the linearity and reducing the input-referred noise of the bootstrapped bulk-driven MOS transistor, which results in an improvement of the overall performance of the transconductor. The center frequency of the bandpass filter designed can be programmed in the frequency range from 6.5 kHz to 37.5 kHz with a power consumption ranging between 1.34 $\mathsf{\mu }$W and 2.19 $\mathsf{\mu }$W. The circuit presents an in-band integrated noise of 190.5 $\mathsf{\mu }$V${}_{rms}$ and is able to process signals of 110 mV${}_{pp}$ with a THD below −40 dB, thus leading to a dynamic range of 47.4 dB. Full article

In this paper, we analyze the effects of channel leakage on the design, modelling and characterization of a high voltage pseudo-floating gate amplifier (PFGA) used as sensor front-end. Leakages are known as a major challenge in new modern CMOS technologies, which are used to bias the PFGA, and consequently affect the behavior of the amplifier. As high voltages are desired for actuation of many types of resonating sensors, especially in ultrasound applications, PFGA implemented in high voltage and low leakage technologies, such as older CMOS fabrication processes or power MOSFET can be the only option. The challenge with these technologies used to implement the PFGA is that the leakages are very low, which affect the biasing of the floating gate. However, the numerous advantages of this type of amplifier, implemented with modern fabrication processes, such as high flexibility, compactness, low power consumption , etc. encouraged the authors to research about this topic. This work provides analysis of the working principle and the design rules for this amplifier, emphasizing the major differences between PFGA implemented in low leakage and high leakage technologies. Static and dynamic analysis, input offset and non-linearity of the PFGA are the main topics of this article. Three different design approaches are presented in this paper, in order to provide a more general design procedure and offset compensation for any low leakage PFGA. The amplifier has been simulated in AMS- $0.35\mu m$ CMOS models for supply voltages of 5 V and 10 V. Two prototypes have been realized to verify the validity of the modelling and the simulation results. Both devices have been realized by using discrete components and mounted on a printed circuit board. In this work, MOSFETs are realized by using commercial IC CD4007UB and 2N7000. Measurement results of the first prototype proved that the implementation of a low leakage PFGA is possible after that the input offset of the amplifier has been compensated. Measurement results of the second prototype have been used to characterize the low leakage PFGA, extracting the best performances from this amplifier, realized with less components and providing a more compact device. Finally, design rules have been summarized in order to implement this amplifier, which enjoys compactness and a relative low power dissipation. Full article

In this paper, we characterize and model a bidirectional front-end based on pseudo-floating gate amplifier (PFGA) for actuation and read-out of resonating sensors. The basic idea consists of swapping the power supply of the PFGA in order to change the directionality of the front-end. A detailed description of the system has been discussed in this paper and supported by simulations and measurement results. A prototype has been fabricated using discrete components and tested with a real transducer (Murata MA40S4) and a Butterworth Van Dyke (BvD) load, which has proved to be proved to be a well approximated model for resonant sensors. The bidirectional amplifier has been implemented with the integrated circuit CD4007UB, which is a commercial discrete component containing low leakage MOSFET. The values chosen for the BvD load are $R_b=330$ $\Omega$ , $L_m=60$ mH, $C_s=450$ pF, $C_E=2.2$ nF, which are approximately the same values of the lumped parameters reported in the data-sheet of the real sensor. This transducer is characterized by a nominal resonant frequency of 40 kHz. Measurement results show good fitting with the models developed in this work and the possibility to predict the sensor response by using the BvD load. Full article